"We've been told about people who are not answering their phones, but you have to understand that there are people who are out of town and on holiday."

Fire officials say around 30 buildings in the town centre were destroyed, some by the initial blast and others by the subsequent fire.

"When you see the centre of your town almost destroyed, you'll understand that we're asking ourselves how we are going to get through this event," a tearful town Mayor Colette Roy-Laroche told a televised news briefing.

Police say some cars spilled their oil contents into the river that runs through the town.

"We're working on the assumption that all the cars were pressurised and could explode, that's why progress is slow and tough," local fire chief Denis Lauzon said.

The rail line is operated by Montreal, Maine & Atlantic, which owns some 820 kilometres of track in Maine and Vermont in the United States and in Quebec and New Brunswick in Canada.